This relates generally to electronic devices with displays, and, more particularly, to displays with backlights.
Electronic devices such as computers and cellular telephones have displays. Some displays such as plasma displays and organic light-emitting diode displays have arrays of pixels that generate light. In displays of this type, backlighting is not necessary because the pixels themselves produce light. Other displays contain passive pixels that can alter the amount of light that is transmitted through the display to display information for a user. Passive pixels do not produce light themselves, so it is often desirable to provide backlight for a display with passive pixels.
In a typical backlight assembly for a display, a light guide plate is used to distribute backlight generated by a light source such as a light-emitting diode light source. Optical films such as a diffuser layer and prism films may be placed on top of the light guide plate. A reflector may be formed under the light guide plate to improve backlight efficiency.
A strip of light-emitting diodes may provide light to an edge of a light guide plate. Light scattering features such as bumps may be provided on the light guide plate. Light from the light-emitting diodes that is traveling within the light guide plate may be scattered upwards by the bumps to form backlight for a display. Light guide plates may also sometimes be provided with elongated ridges (sometimes referred to as lenticular features) that help extract backlight from the light guide plate. The ridges are provided in a uniform rectangular region on the light guide plate.
Light from the strip of light-emitting diodes is initially concentrated in the vicinity of the outputs of the light-emitting diodes. The light must travel a sufficient distance into the light guide plate to mix enough to be used as backlight illumination. Backlight units that require large mixing distances may consume more volume within a display than desired. At the same time, reducing the mixing distance in a backlight too much may lead to undesired backlight hotspots.
It would therefore be desirable to be able to provide displays with improved backlights.